A disc changer is known which is capable of carrying a plurality of discs such as CDs or DVDs mounted thereto and playing the discs successively.
An example of such disc changer includes a roulette table having a disc-like shape and formed, at the periphery, with plurality of mount portions to which a plurality of discs are to be mounted, a tray for rotatably supporting the roulette table and moving the periphery (formed with the mount portions) of the roulette table into and out of the main body of the changer, and a pick-up unit arranged at a predetermined position (hereinafter referred to as a “reading position”) on a path along which the periphery of the roulette table rotates. With the tray accommodated in the main body, the roulette table is rotated, and the pick-up unit clamps the disc transported to the predetermined reading position to read the data recorded on the disc.
Further, a disc changer is known in which the driving source for the in/out operation of the tray and the clamping/releasing operation of the pick-up unit comprises a single electric motor and a driving force transmission mechanism for transmitting the driving force of the electric motor selectively to the pick-up unit and the tray. For example, JP-A 2002-184080 discloses a disc changer which includes a driving force transmission mechanism comprising a rack formed on the tray and extending in the back and forth direction, a pinion for meshing with the rack, a cylindrical cam having a circumferential surface part of which is formed with a guide groove inclining vertically and another part of which is formed with teeth, and two-stage gear unit consisting of a large-diameter gear for meshing with the pinion and a speed reduction gear and a small-diameter gear partially formed with teeth for meshing with the teeth of the cylindrical cam.
In the disc changer, the driving force of the electric motor is transmitted to the large-diameter gear via the speed reduction gear, and the rotational force of the large-diameter gear is converted, by the large-diameter gear, the pinion and the rack, into the force for straight movement in the back and forth direction and transmitted to the tray. Further, by the cylindrical cam and the small-diameter gear rotating along with the large-diameter gear, the rotational force of the small-diameter gear is converted into the force for straight movement in the up and down direction and transmitted to the pick-up unit.
FIGS. 29 and 30 show another known driving force transmission mechanism in which a crank arm 700, a guide groove 1100 formed at a lower surface of a tray 1000, and a cylindrical cam 800 transmit the driving force of a single electric motor 500 to the tray 1000 and to pick-up unit (not shown) while switching therebetween.
FIG. 29 shows the state in which the tray 1000 is accommodated in the disc changer, whereas FIG. 30 shows the state in which an end of the tray 1000 is pulled out of the disc changer.
It is to be noted that the electric motor 500 as the driving source, a speed reduction mechanism 600 for transmitting the driving force of the electric motor 500 to the crank arm 700, the crank arm 700 and the cylindrical cam 800 are arranged below the tray 1000, i.e. on the deeper side with respect to the sheet surface. However, for convenience of drawing of the figure, the electric motor 500, the speed reduction mechanism 600, the crank arm 700 and the cylindrical cam 800 are drawn with solid lines in FIGS. 29 and 30.
Though not illustrated in FIGS. 29 and 30, the pick-up unit in the form of a box is disposed in a recess formed at an upper left portion of the tray 1000. The pick-up unit has a surface facing the cylindrical cam 800 and provided with a lever projecting from the surface. The distal end of the lever is fitted in a cam groove (not shown) formed on the circumferential surface of the cylindrical cam 800 as to be inclined to the vertical (in the direction perpendicular to the sheet surface).
The driving force of the electric motor 500 is transmitted to the crank arm 700 by the speed reduction mechanism 600. When the crank arm 700 rotates by the driving force of the electric motor 500, the distal end 710a of the arm portion 710 moves along the guide groove 1100 formed at the lower surface of the tray 1000. The guide groove 1100 includes an arcuate, intermediate curve 1110 having a radius of curvature equal to the radius of gyration of the arm portion 710, and a left and a right straight ends 1120 and 1130 extending from opposite ends of the intermediate curve 1110.
When the distal end 710a of the arm portion 710 moves along the intermediate curve 1110 of the guide groove 1100, the rotational force of the crank arm 700 is not transmitted to the tray 1000 but transmitted only to the cylindrical cam 800 during when the cylindrical cam meshes with the crank arm 700. When the distal end 710a of the arm portion 710 moves along the left straight end 1120 or the right straight end 1130 of the guide groove 1100, the crank arm 700 disengages from the cylindrical cam 800. Therefore, the rotational force of the crank arm 700 is not transmitted to the cylindrical cam 800 but transmitted only to the tray 1000.
As noted above, in the disc changer shown in FIGS. 29 and 39, the structure to utilize the driving force of a single electric motor for both of the in/out operation of the tray 1000 and the disc clamping/releasing operation of the pick-up unit is realized by dividing the range of rotation of the crank arm to transmit the driving force of the electric motor into the range for driving the tray and the range for driving the pick-up unit. Also in the disc changer disclosed in JP-A 2002-184080, the rotation range of the two-stage gear is divided into the range for driving the tray and the range for driving the pick-up unit, and the mechanism for transmitting the driving force of the single electric motor is basically the same as that shown in FIGS. 29 and 30.
In the structure disclosed in JP-A 2002-184080, the driving force transmission mechanism for transmitting the driving force of the electric motor to the tray and the pick-up unit by utilizing the two-stage gear is complicated and requires a large number of parts. As compared to this, the driving force transmission mechanism using a crank arm shown in FIG. 29 utilizes a simple gear structure and a less number of parts, and hence, is advantageous as the driving force transmission mechanism of a disc changer.
However, in the conventional driving force transmission mechanism utilizing a crank arm, the guide groove 1100 comprises an arcuate, intermediate curve 1110 and a left and a right straight ends 1120 and 1130 connected to opposite ends of the intermediate curve. Therefore, when the distal end 710a of the arm portion 710 moves from the intermediate curve 1110 to the left straight end 1120 or the right straight end 1130, a large rotational force is suddenly transmitted from the crank arm 700 to the tray 1000. On the other hand, when the distal end 710a of the arm portion 710 moves from the left straight end 1120 or the right straight end 1130 to the intermediate curve 1110, the rotational force which has transmitted from the crank arm 700 to the tray 1000 suddenly disappears. Therefore, the tray 1000 cannot move smoothly at the start of the movement and the end of the movement.
Further, when the distal end 710a of the arm portion 710 is rotated counterclockwise from the state shown in FIG. 29 so that the distal end 710a of the arm portion 710 reciprocates through the left straight end 1120 of the guide groove 1100 and reaches the boundary between the end and the intermediate curve 1110, the distal end 710a of the arm portion 710 has difficulty in moving to the intermediate curve 1110. Therefore, the crank arm 700 need be stopped at this position. The stop position of the crank arm 700 corresponds to the position at which the pull-out amount of the tray 100 becomes maximum. When a crank arm 700 having a shorter arm length is used, the guide groove 1100 of the tray 1000 need be formed closer to the crank arm 700, so that the maximum pull-out amount of the tray 1000 is reduced. Conversely, in the conventional driving force transmission mechanism using a crank arm, to increase the maximum pull-out amount of the tray 1000, the arm length of the crank arm 700 need be increased, which leads to an increase in the size of the crank arm 700.
Further, in the method in which the driving force of the single electric motor 500 is transmitted to the crank arm 700 and the object to which the driving force is transmitted is switched between the tray 1000 and the pick-up unit depending on the rotation range of the crank arm 700, the operational states of the disc changer (such as a disc changing state, a disc clamping state or a disc playing state) are related with the rotation-l position of the Frank arm 700. Therefore, to control the operation of the disc changer, the rotational position of the crank arm 700 need be detected to utilize the detection signals for the control.
For example, at least four operational states need be detected, i.e., (1) the state in which the tray is pulled out of the housing (hereinafter referred to as the “open stop position”), (2) the state in which the tray is completely accommodated in the housing (hereinafter referred to as the “close stop position”), (3) the state in which the pick-up unit is clamping a disc (hereinafter referred to as the “clamp position”), and (4) the state in which the pick-up unit is not clamping a disc (“clamp release position”). To detect these, it may be considered to provide switches at the open stop position and the close stop position of the tray, and the clamp position and the clamp release position of the pick-up unit, for example. In this method, however, a large number of switches need be provided at widely separated positions.
As another method for detecting the rotational position of the crank arm, it may be considered to attach, to the crank arm, a rotary encoder generally known as a device for detecting the rotational position of a rotating object.
However, in the driving force transmission mechanism of the above-described disc changer, the rotation range of the crank arm 700 is about ±150° taking the state shown in FIG. 29 as the reference direction, and it is only necessary to divide the rotation range into several regions and determine at which one of the regions the crank arm 700 locates. However, a rotary encoder can detect angles with accuracy which is unnecessary high for the above purpose, and accordingly is expensive. Therefore, to reduce the cost as much as possible, the use of a rotary encoder is not desirable.